This invention relates to method and apparatus for establishing an A.C. electrical field in a subsurface oil or mineral bearing formation and establishing in response to the electrical field a zone of electrochemical activity resulting in electrochemical reactions with constituent elements of the earth formation for increasing the internal pressure of the earth formation over an area greatly exceeding the zone of electrochemical activity.
Until fairly recent times, it was relatively easy to find new oil reserves when a field was depleted or became unprofitable. In many fields only 15%-25% of the oil in place was actually recovered before reservoir pressure or drive was depleted or other factors made it uneconomical to continue to produce the field. As long as new reserves were readily available, old fields were abandoned. However, with the crisis now confronting the domestic oil industry, coupled with the fact that most of the existing on-shore oil in the United States has already been discovered, it is obvious that such known reserves must be efficiently and economically produced.
It has been estimated that at least 50% of the known oil reserves of the United States cannot be recovered using conventional pumping methods. A substantial amount of this oil is of an abnormally low gravity, and/or high viscosity, often coupled with the fact that there is little or no pressure in the oil-bearing formation. In the absence of formation pressure, even oil of average viscosity and gravity is difficult to produce without adding external energy to the formation to move the oil into a producing borehole. Accordingly, a great deal of attention has recently been given to various methods of secondary recovery. Water flooding has been utilized with mixed results to attempt to increase the natural reservoir pressure hydraulically. Thermal flooding techniques, such as fire flooding, steam injection and hot water flooding have been utilized to alter the viscosity of the oil and hence, enhance its flow characteristics. However, none of these thermal techniques contributes to increasing the formation pressure and have been successful only in a limited number of applications. All of the methods mentioned above require extensive, and quite expensive, surface installations for their utilization.
The prior art contains patents that have introduced electrical currents into a subsurface oil- or mineral-bearing formation for the express purpose of heating the formation in order to lower the viscosity and stimulate the flow of the oil or mineral in the immediate area involved in the heating process. Examples of such patents are: U.S. Pat. No. 849,524 (Baker, 1907); 2,799,641 (Bell, 1957); 2,801,090 (Hoyer, 1957); 3,428,125 (Parker, 1969); 3,507,330 (Gill, 1970); 3,547,193 (Gill, 1970); 3,605,888 (Crowson, 1971); 3,620,300 (Crowson, 1971), and 3,642,066 (Gill, 1972). All of the above patents depend in some form on electrothermic action to enhance the flow characteristics of the oil or an "electro osmosis" action whereby the oil tends to flow from an electrically charged positive region to a negatively charged region. However, none of the above patents suggests the establishment of a zone of electrochemical activity wherein an electrochemical reaction is promoted with constituent elements of the formation, salt water and oil, for increasing the internal pressure of the formation over an area greatly exceeding the zone of electrochemical activity.
Accordingly, one primary feature of the present invention is to provide method and apparatus for establishing a zone of electrochemical activity in a subsurface formation resulting in electrochemical reactions with constituent elements of the formation, such as salt water and oil, for generating volumes of gas in the formation for increasing the formation pressure.
Another feature of the present invention is to provide method and apparatus for establishing a zone of electrochemical activity in a subsurface formation for enhancing the flow characteristics of oil in the formation by lowering the viscosity of the oil.
Yet another feature of the present invention is to provide method and apparatus for establishing a zone of electrochemical activity in a subsurface formation for releasing salt water and oil in situ from the formation matrix within the zone of electrochemical activity and separating the oil and salt water within the earth formation matrix by gravitational action.
Still another feature of the present invention is to provide method and apparatus for establishing an electric field within the subsurface formation wherein a plurality of electrodes is employed, each of the electrodes projecting into the formation through one of a plurality of spaced boreholes and an insulating means is utilized for insulating each of the electrodes from the earth structure surrounding the borehole for preventing an electrical current path between the electrode and the earth structure and isolating the electrical current path from the electrode into the earth formation.